Can't change time signature?

I'm writing a track in 4/6 time. When I change the time signature in the transport bar, the notes change but the grid of the MIDI editor piano roll wont. It kind of takes an average and will make some beats have more grid lines than others. After playing around with the grid controls, the lines for each beat & measure are part way through each grid segment. Not sure why this is happening - it was really simple & easy in Fruity Loops :/ Thanks

Change the grid to triplet at the bottom of the MIDI editor. Non-Dyadic Time Signatures

Yep, that's right. I think I can also get it to work by using 1/24 grid. Thanks ;)